Abstract The yellow ligaments of the spine are charac- terized by an exceptionally high content of elastin, a pro- tein with a proved longevity in several human tissues. This unique biochemical composition suggested a suitability of yellow ligaments for age estimation based on aspartic acid racemization (AAR), which was tested by determination of AAR in total tissue specimens and in purified elastin from yellow ligaments of individuals of known age. AAR was found to increase with age in both sample sets. The purified elastin samples exhibited a much faster kinetics than the total tissue, with ca. 3.7–4.6-fold higher apparent rates. The relationship between AAR and age was much closer in the purified elastin samples (r =0.96–0.99) and it can therefore be used as a basis for biochemical age esti- mation. The analysis of total tissue samples cannot be rec- ommended since the AAR values can be strongly influ- enced even by slight, histologically non-detectable varia- tions in the collagen content. Age estimation based on AAR in purified elastin from yellow ligaments may be a valuable additional tool in the identification of unidenti- fied cadavers, especially in cases where other methods cannot be applied (e.g. no available teeth, body parts). Keywords Age estimation · Aspartic acid racemization · Yellow ligaments · Elastin Introduction Biochemical age estimation based on aspartic acid racemi- zation (AAR) is gaining acceptance in forensic practice as a method which is both highly accurate and repro- ducible, as stated by numerous publications of different groups (e.g. Fu et al. 1995; Mörnstad et al. 1994; Ogino et al. 1985; Ohtani 1995a, 1995b; Ohtani and Yamamoto 1987; Ritz et al. 1990, 1993, 1995; Ritz-Timme 1999; Ritz- Timme et al. 2000a; Rösing and Kvaal 1998). AAR is an inevitable consequence of the physiological ageing of proteins (for details see Ritz-Timme and Collins 2002). It represents one of the major types of non-enzymatic cova- lent modification of proteins which are synthesized using only one optically active form of amino acids, laevo or L-amino acids. In vivo racemization can be observed in numerous proteins of different human tissues (Ritz- Timme and Collins 2002). It leads to an age-dependent accumulation of D-aspartic acid in long-living human proteins 1 which is the basis of the biochemical age esti- mation. Routinely, age estimation based on AAR is performed by analysis of dentine. Dentine is an “ideal” tissue for bio- chemical age estimation because of its high content of long-living proteins and its relatively stable biochemical composition. However, in forensic practice teeth are not always available. The suitability of non-dental tissues for age estimation based on AAR has been tested. In the tis- sues investigated so far, biochemical age estimation in to- tal tissue specimens and crude protein extracts is associ- ated with a much reduced accuracy in comparison to den- tine (Ohtani et al. 1998; Pfeiffer et al. 1995a, 1995b; Ritz and Schütz 1993; Ritz et al. 1994). Accurate results can only be achieved by analysis of purified long-living pro- teins, which usually requires highly sophisticated method- ologies (Ritz et al. 1996). The necessity of protein purifi- S. Ritz-Timme · I. Laumeier · M. Collins Age estimation based on aspartic acid racemization in elastin from the yellow ligaments Int J Legal Med (2003) 117 : 96–101 DOI 10.1007/s00414-002-0355-2 Received: 23 July 2002 / Accepted: 30 October 2002 / Published online: 28 February 2003 ORIGINAL ARTICLE S. Ritz-Timme (✉) · I. Laumeier Institut für Rechtsmedizin der Christian-Albrechts-Universität zu Kiel, Arnold-Heller-Strasse 12, 24105 Kiel, Germany, Tel.: +49-431-5973634, Fax: +49-431-597 3612, e-mail: s.ritz@rechtsmedizin.uni-kiel.de M. Collins Fossil Fuels and Environmental Geochemistry, University of Newcastle upon Tyne, Newcastle NE3 1UH, UK, © Springer-Verlag 2003 1 In proteins the so-called racemization of aspartic acid (AAR) in- volves both aspargine and aspartic acid that decompose via a suc- cimide ring to the same four residues, namely L-aspartyl, D-aspartyl, L-isoaspartyl and D-isoaspartyl, all of which are in chemical equilib- rium via the succimide ring (for overview see Ritz-Timme and Collins 2002). Asparingyl, aspartyl, isoaspartyl and succinimidyl residues, are all converted to free aspartic acid during acid hydrolysis, a preparative step in chromatographic amino acid analysis for biochemical age esti- mation.